The present invention relates to an image recording apparatus for recording an image using a semiconductor laser as an exposure light source and a semiconductor laser driving circuit applied thereto.
As for a semiconductor laser driving circuit, there are generally known a circuit including an automatic power control (APC) circuit used to feed back an output light amount of a light beam emitted from a semiconductor laser to control the output light amount of the light beam emitted from the semiconductor laser to be constant, and a circuit including an automatic current control (ACC) circuit used to feed back an amount of current caused to flow through the semiconductor laser to control the amount of current to be constant, thereby controlling an output light amount of the light beam from the semiconductor laser to be constant.
Either of the semiconductor laser driving circuit including the APC circuit and the semiconductor laser driving circuit including the ACC circuit includes an error amplifier for amplifying and outputting a difference (error) between a command signal in accordance with which turn-ON/turn-OFF of a semiconductor laser is controlled so that the semiconductor laser emits a light beam with a predetermined output light amount and a signal which is fed back from the semiconductor laser. The semiconductor laser is driven based on an output signal from the error amplifier, thereby allowing the semiconductor laser to invariably emit a light beam with a predetermined output light amount.
However, in the conventional semiconductor laser driving circuit, a consumed electric power of the above-mentioned error amplifier changes between the turn-ON state and the turn-OFF state of the semiconductor laser. For this reason, there arises a problem in that temperature drift is generated in the output signal from the error amplifier due to a temperature change caused by self-heating of the error amplifier, and thus the output light amount of the light beam from the semiconductor laser fluctuates. However, the fluctuation in the output light amount of light beam from the semiconductor laser due to the temperature drift in the output signal from the error amplifier cannot be controlled using the APC circuit or the ACC circuit.
Hence, an image recording apparatus for recording an image using the above-mentioned semiconductor laser driving circuit involves a problem in that the output light amount of the light beam from the semiconductor laser fluctuates in correspondence to the temperature drift in the output signal from the error amplifier, and thus an image quality of a recorded image is reduced.
In addition, in the conventional semiconductor laser driving circuit, there is also encountered a problem in that when the semiconductor laser driving circuit is influenced by an extraneous electric wave which is radiated from a mobile telephone, a wireless local area network (LAN) or the like, which has a high carrier frequency, and which is modulated with a frequency equal to or lower than an image frequency (a driving frequency for the semiconductor laser), the extraneous electric wave is demodulated in the semiconductor laser driving circuit to be outputted in the form of noises and thus the output light amount of the light beam from the semiconductor laser fluctuates.
In this case, similarly, there arises a problem in that the output light amount of the light beam emitted from the semiconductor laser fluctuates, and the image quality of the image recorded by the image recording apparatus deteriorates.
Note that it is a problem firstly posed by an inventor of the present invention that the output light amount of the light beam from the semiconductor laser fluctuates due to the temperature drift in the output signal from the error amplifier, and thus any of the conventional techniques is not associated with the present invention. This is also applied to the influence by the extraneous electric wave.